feat: add semantic admin palette

src/lib/theme-contrast.ts

@@ -3,6 +3,58 @@ type Rgb = readonly [number, number, number];
 export type PublicThemeColors = Record<string, string>;
 export interface ContrastPair { name: string; foreground: string; background: string }
 
+export interface AdminPalette {
+  canvas: string;
+  surface: string;
+  surfaceElevated: string;
+  text: string;
+  muted: string;
+  border: string;
+  accent: string;
+  accentText: string;
+  accentForeground: string;
+  success: string;
+  warning: string;
+  error: string;
+  info: string;
+  sidebar: string;
+  sidebarText: string;
+  overlay: string;
+  focusRing: string;
+}
+
+export function deriveAdminPalette(colors: PublicThemeColors): AdminPalette {
+  const publicBackground = colors.color_background ?? "#f8fafc";
+  const blackRatio = contrastRatio("#000000", publicBackground) ?? 21;
+  const whiteRatio = contrastRatio("#ffffff", publicBackground) ?? 1;
+  const dark = whiteRatio > blackRatio;
+  const canvas = dark ? "#0b0f19" : "#f1f5f9";
+  const surface = dark ? "#151b27" : "#ffffff";
+  const surfaceElevated = dark ? "#1e2635" : "#f8fafc";
+  const text = dark ? "#f8fafc" : "#0f172a";
+  const muted = dark ? "#a8b3c7" : "#475569";
+  const accent = colors.color_primary ?? "#f59e0b";
+  return {
+    canvas,
+    surface,
+    surfaceElevated,
+    text: readableColor(text, [canvas, surface, surfaceElevated]),
+    muted: readableColor(muted, [canvas, surface, surfaceElevated]),
+    border: dark ? "#334155" : "#cbd5e1",
+    accent,
+    accentText: readableColor(accent, [canvas, surface, surfaceElevated]),
+    accentForeground: readableColor("#ffffff", [accent]),
+    success: dark ? "#4ade80" : "#15803d",
+    warning: dark ? "#facc15" : "#a16207",
+    error: dark ? "#f87171" : "#b91c1c",
+    info: dark ? "#38bdf8" : "#0369a1",
+    sidebar: dark ? "#101622" : "#172033",
+    sidebarText: "#f8fafc",
+    overlay: "rgba(2, 6, 23, 0.72)",
+    focusRing: accent,
+  };
+}
+
 export function derivePublicForegrounds(c: PublicThemeColors) {
   const value = (key: string, fallback: string) => c[key] ?? fallback;
   const background = value("color_background", "#f8fafc");